Voltage two-tone source



7 p 1949- v v E. R- SHENK 2,432,561

VOLTAGE TWO-TONE SOURCE a Filed March 19, 1946 2 Sheets-Sheet l Fly .1 ""41 TWO TONE v 2 I .3 v mmumcr SH/FTED f 47%? FREQUENCY 5 W4 l EFORM DIV/DER 4 coumous/z Alllll.

g, Y INVENTQR 1 INPUT EUGENE R. SHENK ATTORNEY v Sept. 20, 1949- E. R. SHENK I 2,

' VOLTAGE TWO-TONE SOURCE Filed March 19, 1946 2 Sheets-Sheet 2 AA'A'AQA'A' n 4- A A A A A SIGNAL LINES INVENTOR 27*5 EUGENE I SHENK ATTORNEY related in steps aredesirable.

fiatented Sept. 2Q, l94

VOLTAGE'TWO-TONE SOURCE Eugene R. Shenk, Brooklyn, N. Y., assignor to a Radioecorporation of America, a. corporation of Delaware 7 Application March is, 1946, Serial No. 655,440

This application relates to tone generators and in particular to means for producingoscillations of two frequencies. The means of the present invention is of wide application in the radio and allied arts. In the embodiment used to illustrate my invention a telegraphy-system is shown. The system shown may also be used for generation of tones representing black'and white in a subcarrier frequency modulation facsimile transmission. In telegraphy one tonefrequency is used to indicate marking intervalsand a different tone frequency is used to indicate spacing intervals. In many other applications, for example; subcarrier frequency modulation black and white facsimile, it is necessary to key between two tone frequencies at signalling rate, and then one tone represents black and the other white in the picture. T

Various methods and means'for producing two tones (may be superaudibie) frequencies-for the purpose described above are-'knownin the prior art. In these known systems, however, usually a large amount of transient energy is generated at the frequency shift points, i. e., when changing from one frequency to the other. I

Heretofore thekeying fromonetone frequency to another has been accomplished by makin'g both tones continuously available and then' se= lectively choosing between the tones by means of an elaborate electronic switchingmeans. Even the best of such arrangements have Zbeenubeset with switching transients to somedegree This adds to the useful tones many unnecessary side tones and frequencies which then have to be eliminated.

The primary object of this invention is to provide a very simple and straightforward method of and means for producing two-tone keying with no transient at the frequency shift points. These general objects are attained in accordancewith the present invention by use of a multivibrator or any other kind of a frequency divider driven or controlled by a source of oscillationsv of a frequency f to be divided. Preferably the frequency f is a multiple of the two desired tone frequencies for use at the two-tone output. The order of division of the divider is changed to change from one tone frequency to another tone frequency. This order of divisionis related as desired to the signalling potentials.

In some applications, for example in multiplex telegraph systems or to designate several picture shades, oscillations the frequencies of which are A further :object of my invention is'to provideany selected one of 16 Claims. (Cl. 250-36) aplurality of oscillating voltages of discrete fre-- quencies related-as desired each to theother and free of transients-at the-frequency shift points. This object is attained by usevof'a fre'quencydivider controlled by'oscillating voltage'themag; nitude of which is varied in steps by appropriate control potentials. Then the 'output of the divider' will change in frequency insteps as the control voltage magnitude changes in steps. In describing my invention in detail reference willbe'made to the attached drawings wherein Fig lillustrates schematically and by block diagram atone keyer arranged in accordance with my invention.

Fig. 2 illustrates by circuit element and circuit element connections a system for generating two tones alternately produced in the presence of signalling and representing different signalling conditions;

Figs. 2a and 2b are modifications of the ar-' rangement of-Fig. 2; while Fig. 3 is a further embodiment of my improved two-tone keyer. fl j V 1 in Fig. 1 the'bo c I represents a source of oscillationsof say sinusoidal wave form and of frequency f. The rectangle 2 includes a wave current amplitude and wave form controllingnet' work and is shown as being connected toa keying input whereat the signals areflapplied. 1 This showing is diagrammatic as will be seen from the detailed discussion of the following figures; The amplitude'limited and formed voltages of frequency f are supplied to the rectangle 3 wherein is included a-frequency divider having as an output 'twotone frequencies alternately present in accordanc'e'with the efiectiveness of the keying input to shift the frequency of operation of the divider between the said two tones. The keying input wave may consist'of a direct current voltage which varies in-amplitude and/or polarity in accordance with signal voltage. The whole arrangementis such that the amplitude of the voltage offrequency ,1 which is supplied tothe frequency divider in 3 is under control of the keying input voltage. The frequency divider is so constituted as to be sensitive to the amplitude of the controllingvoltage supplied thereto, 1. 'e., the order of count of the frequency divider depends upon the amplitude of the controlling voltage supplied from unit 2 to unit 3.

Now turning to "Fig. 2, wherein the essential elements of a practical embodiment are shown, tubes VI and V2 are in the frequency divider circuit of rectangle 3 of Fig. 1. This frequency divider is shown as being of the multivibrator type and cults connected in parallel and with separate controlling voltages supplied to their control grids. Such an arrangement is illustratedin Fig. 2b. With such-a system the location of the tones in the frequency spectrum may be readily shifted. Several channels may be used and their frequency locations exchanged in accordance with some coded signal. Some degree of secrecy may be obtained in this manner. The embodiment of Fig. 2b is a modification of Figs. 2 and 2a. In this modification the tube V5 is replaced by a plurality of tubes V5, for example 3, with their output circuits in parallel. Each tube V5 has its cathode grounded and has in series with its anode a resistor I4 as in the prior figures, and the resistors l4 have their ends remote from the tube anodes tied together and connected to the positive terminal of the source through resistor 16. These ends of the parallel resistors I4 are also,coupled by condenser C2 to potentiometer resistor P2. The grid circuits of the tubes V5 of Fig. 2b are separated and are biased by separate grid biasing resistors connected to bias source 21. The grids of the tubes are individually and separately supplied by control potentials or signals over lines #l,#2 and #3. The control potentialsare shown as appearing sequentially (in time), and it will be understood that the sequence of the potentials on lines #I, #2 and #3 may be arranged as desired. The tube V5 of Fig. 2a in'the embodiment of Fig. 2b is likewise replaced by three tubes V5, and these tubes have their anodes connected in parallel by resistors l4", and to the direct current source by resistor l6, and to the potentiometer Pl by condenser Cl. These tubes also have their grids in separate circuits supplied by potentials over lines #4, #5 and #6, and these potentials may be supplied in any sequence as desired. The sequence followed may be a continuation of the sequence in which potentials are applied over thelines #I, #2 and #3. The potentials may represent signals or control potentials of any desired nature and may be for sending messages or for producing oscillations of tone frequency the frequencies of which may be changed in steps as desired, and which are subharmonically related to the oscillations of frequency f.

Another method and means of carrying out the invention is shown schematically in Fig. 3 of the drawings. Here the tube V1 has its anode and control grid regeneratively coupled by windings of a transformer T. The anode winding is connected to the positive terminal of the source E. The grid winding is connected to a point on the resistance of a potentiometer Pl across which is applied a negative biasing source EC. The arrangement is such that the bias on the grid of the tube V1 may be adjustedbeyondcutoff, the extent of this bias being used to set the count or order of division to determine the frequency of operation of the regenerative oscillator. The cathode of the tube V1 is coupled to ground through the impedance of diodesii) and 60 thereby supplying the direct current circuits through the tube V1 between the cathode and the anode and between the cathode and the grid. The condenser C5 is coupled between the cathode of tube V1 and ground. The source of ocsillations I0 is now supplied to a current amplifying and current amplitude limiter tube V 8 similar to V6 of Fig. 2, and from the limiter V8 through a coupling condenser C6 to the cathode of diode 50 and to the anode of diode 60. The anode of tube V8 is coupled to the positive terminal of the source E by a resistor 52, while the anode of the modulator tube V5 is coupled to the positive terminal of this source by resistors 52 and i4, and to the anode of tube V8 by resistor l4.

The tube V1 with its regenerative circuit T and diodes 50 and 60 and condenser C5 is connected in a counter circuit. The frequency of operation of this circuit depends on thegrid bias and on the rate at which condenser 05 can charge up (through resistance 52, condenser C6 and diode 50), to a point at which it energizes oscillator tube V1 and discharges through diodes 60 and 50. The synchronizing voltages fed through coupling condenser C5 are applied to the anode of diode 60 and being negative do not leak off. They are, however, also supplied to the cathode of diode 50 and this diode passes the voltages to charge the condenser C5. The potentiometer PI is used to adjust the grid bias of tube V1 sumciently beyond the plate current cutoff value to secure the desired count.

If now tube V5 is caused to changefrom the conductive condition, at which say zero potential representing mark might be applied to the control grid thereof, to the non-conductive condition at which a high negative potential might be applied to the control grid thereof, the effective plate supply voltage to the tube V8 increases,- as does the magnitude of the synchronizing voltages fed to condenser C6. Consequently, the charge supplied to the capacitor C5 on each cycle of the oscillator frequency 1 increases and the number of charges or cycles or steps required to make the cathode of tube V1 sufiiciently nega'-' tive to render tube V1 conductive decreases. Obviously the number of cycles of the frequency f required to charge the condenser C5 to a point at which tube V1 conducts is larger when tube V5 is conducting than when tube V5 is nonconducting. Thus the rate of oscillation of tube V1 is of one value when tube V5 is conducting and is of a higher value when the tube V5 is non-conducting.

What is claimed is:

1. In a wave generator, a frequency divider including an electron discharge tube in a controlled oscillation generating circuit, a source of oscillating voltages coupled to said divider to entrain it to operate at a fundamental frequency which is a subharmonic of the frequency of said voltages, the factor of division of the divider depending in part on the tube circuit constants and the magnitude of the applied controlling voltages, an amplifier in said coupling, a source of potentials which varies in magnitude by steps, and means for controlling the gain of said amplifier in accordance with said potentials to correspondingly control the magnitude of the volt ages controlling the frequency divider to corre-; spondingly vary the fundamental frequency of the produced oscillatory energy.

2. In a telegraphy system, a frequency divider including two tubes in a multivibrator circuit, a source of oscillating voltages coupled by separate paths to the two tubes of the multivibrator to entrain the same to operate at a fundamental frequency which is subharmonically related to the frequency of said voltages, the factor of division of each tube of the divider depending. in part on the tube circuit constants and the mag--' nitude of the applied voltage, said divider operating to produce oscillatory energy of a frequency determined by the sum of said factors, a source of potential which varies between two values each of which represents a different sig- 7 flailing condition, a current amplitude limiter and amplifier tube in at least one coupling be tween the first mentioned source and the divider tubes, and means for varying the gain of said amplifier tube by potential from said source to correspondingly vary the magnitude of the voltages supplied to one tube of the multivibrator to correspondingly vary the frequency of opera tion of the multivibrator.

3. In a signalling system, a multivibrator. comprising a pair of electron discharge tubes having electrodes interconnected by capacitors and com nected to potential sources by resistors whereby the multivibrat'or oscillates at a frequency de' pending in part on the value of the circuit elements, a source of oscillating voltages of a fre quency which is a multiple of the frequency at which said multivibrator tubes operate, a cur rent amplitude limiter having input electrodes coupled to said source of voltage, an amplifier 3 in a path coupling the output of said current amplitude limiter to a resistor in the circuit of one of said multivibrator tubes, the arrange ment being such that the tubes tend to operate at a fundamental frequency which is a fraction of the frequency of said source, and a source of signal potentials connected to electrodes of said amplifier for modulating the gain of said amplifier to correspondingly vary the fundamental frequency or" operation of the multivibrator.

4, In a two-tone generator a multivibratcr including a pair of electron discharge devices having electrodes interconnected by circuits including resistance and capacity and potential sources, a source of oscillating voltage, a current ampli fier and current amplitude limiter tube having input electrodes coupled to said source, a coupling between the output electrodes of the tube and a circuitsupplying direct current to at least one of the devices in said multivibrator, a modu lating tube having output electrodes associated with the electrodes of said current amplitude limiting tube to control the amplitude of the voltage fed to said one tube of said multivibrator, and means for applying control potentials to said modulating tube.

7-5. '-In a signalling system, a multivibrator comprising a pair of electron discharge tubes having electrodes interconnected by capacitors and connected to potential sources by resistors whereby the multivibrator oscillates at a fre-' quency depending in part on the value of the circuit elements, a source of alternating voltages of a frequency which is a multiple of the frequency at which said multivibrator tubes operate, a current amplitude limiter having input electrodes coupled to said source of voltages, a first amplifier in a first path coupling the output of said current amplitude limiter to .a re "sist'or'in the circuit of one of said multivibrator tubes, a second amplifier in a second path coupling the output of said current limiter tubeto a resistor in the circuit of the other multivibrator tube, the arrangement being such that vthe multivibrator tubes tend to operate at a first fraction of the frequency of said source of volt ages, a source of signal potentials, and means for modulating the gain of said amplifiers in said paths in accordance with said signals where-' by the tubes operate at a second fraction of the frequency of said source.

6-. In a signalling system, an electron dis= charge device having its electrodes'coupled in a regenerative oscillation generating circuit in= eluding a control grid with a variable biasing circuit connected with the same, a charging condenser coupled in the biasing circuitof said device, a source of oscillatory voltage of a frequency higher than the frequency of operation or said oscillation generator, a current amplitude limiter tube having input electrodes coupled' to said source, a coupling between the output electrodes of said current amplitude limiter tube and the biasing circuit of said device, a uni-directional device in said coupling arranged to pass voltage to said condenser to charge the same an amount depending upon the amplitude of the voltage supplied from said source by said tube to said device, a discharge path for said condenser, a source of keying potentials, and means for modulating the gain of said limiter tube in accordance with said keying potential to thereby control the amplitude of the voltage supplied to said charging condenser-andthe frequency of operation of said regenerative generator.

7 Ina multiple tone generator, a multivibrator including a pair of electron dis-charge devices having electrodes interconnected by circuits including resistance and capacity and potential sources azs'ourcelof oscillating voltagesa current amplifier. and current amplitude limiter tube having input electrodes coupled to said source, separate couplings between the output electrodes'of said tube and the two circuits supplying direct cur-rent to the two discharge devices in said lmulti vibrator, a plurality of modulating tubes foreacn coupling, "the modulating tubes of each group having output electrodes connected to the couplingwith which they are associated for ccntrol= lingthe magnitudeof the voltages passed by said couplings, and means for applying control potentials sequentially tolsaid modulating tubes.

8. ,In a frequency shift telegraphy system-, a multivibrator comprising a -pair of electron discharge devices having electrodes interconnected by capacitors and connected, to potential sources by resistors of such avalue that one of the two devices of the multivibrator operates at one fre quency and the other thereof-operates at another frequency, a source of oscillations of a frequency which is a multiple of the frequencies at which said multivibrator devices operate, a current amplitude limiter having input electrodes coupled to said source of oscillations, a first path coupling the output ofsaid current amplitude limiter to a resistor inthe circuit of one of said multivibrator devices, signal amplifying means in saidpath, a second path coupling the output of said current limiter toaresistance in the circuit of the other multivibrator device, a source of signal potentials, and'means'ifor modulatingthe gain of said ampli= 'f-yingmeans tube in said first-named path in accordance with signals.

9.:In apparatus for generating two tones of different-frequencies both of which frequencies are sub=harmonica1ly related to the frequency of oscillatory energy, asource of oscillatory energy ofsubstantiallyconstant frequency Lia frequency divider inc-ludingat leasttone tube in an oscilla tion generating cireuitthe frequency of operation of vwhich depends on the magnitude of a tube electrode "potential, .3, coupling between said source ofoscillatory energy of frequency f and an electrode ofsaid one tube to entrain said divider to operate-at a frequency sub-harmonically "relatedto the frequency of said source, a source'oi control potentials which is keyed in magnitude between two. values, anelectron discharge device having input electrodes coupled to said last 'tubes, and having input named source and having output electrodes connected to said coupling between said source of oscillatory energy of frequency f and said electrode of said one tube, the arrangement being such that when the control potential is of one value the divider operates at one tone frequency sub-harmonically related to the frequency f and when the control potential is of the other value the frequency divider operates at a second tone frequency sub-harmonically related to the frequency f, and an output circuit coupled to said frequency divider.

10. Apparatus as recited in claim 9 wherein said coupling between said source of oscillatory energy of frequency f and said divider includes a voltage limiting tube having an input coupled to the source and having an output coupled to said electrode of the frequency divider tube.

11. Apparatus as recited in claim 10 wherein said coupling between said limiting tube output and said electrode of the frequency divider tube includes a Voltage amplifier tube having input electrodes coupled to the output electrodes of the limiting tube and having output electrodes coupled to said electrode of said divider tube.

12. Apparatus as recited in claim 9 wherein said output circuit includes a filter to select said tone frequencies.

13. In apparatus for generating two tones of different and substantially fixed frequencies which frequencies are sub-harmonically related to the frequency of oscillatory energy of frequency f, a frequency divider including two tubes in an oscillation generating circuit the frequency of operation of which depends on the magnitude of a potential on an electrode of each of said tubes, a source of signals comprising potential keyed between two values, a source of oscillatory energy of frequency f, an amplifier tube having input electrodes coupled to said source of frequency ,f and having output electrodes coupled to an electrode of one divider tube, a second amplifier tube having input electrodes coupled to said source of frequency f and having output electrodes coupled to an electrode in the other of said divider tubes, whereby said divider is caused to operate at a frequenc' sub-harmonically related to the frequency 7', at least one modulator tube having output electrodes coupled to one of the amplifier electrodes coupled to said source of signals to change the magnitude of the potential on an electrode of at least one of said divider tubes to entrain said divider to operate 10 at first and second tone frequencies one representing one signal potential value the other the other signal potential value, and an output circuit coupled to said divider.

14. Apparatus as recited in claim 13 including a second modulator tube having input electrodes coupled to said source ofsignals and having output electrodes coupled to the other amplifier tube.

15. Apparatus as recited in claim 13 wherein said output circuit includes a low pass filter to reject unwanted harmonics and pass said two voltages of said two tone frequencies.

16. In apparatus for generating two tones of different and substantially fixed frequencies which frequencies are sub-harmonically related to oscillatory energy of frequency a frequency divider including two tubes in an oscillation generating circuit the frequency of operation of which depends on the magnitude of a potential on an electrode of each tube, a source of oscillatory energy of frequency a source of signals which vary between two values of potential, a voltage amplitude limiter having an input coupled to said source of oscillatory energy of frequency and having an output coupled by separate paths to an electrode of each of said tubes to apply oscillatory energy of substantially square wave form to said electrodes whereby said divider operates at a frequency sub-harmonically related to the frequency 1, two modulator tubes each having output electrodes in shunt to a different one of said separate paths between said limiter and the electrodes of said frequency divider tubes'and each having input electrodes coupled to said source of signals to apply potentials of different magnitude to said divider tube electrodes to entrain said divider to operate at two tone frequencies one representing one of said signal potential values the other representing the other of said signal potential values.

. EUGENE R. SHENK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

